Information recording media, recording method and recording apparatus

ABSTRACT

Disclosed herewith is a method for enabling fast and high density recording of information. A voltage is applied to a recording layer formed between a pair of electrodes. The distance between the pair of electrodes is set wider at one of land and groove areas of a subject optical disk and narrower at the other or the distance is set so that light absorption occurs only in either of the land and groove areas. The optical disk is also provided with a layer of which light absorption spectrum changes according to the application of an electric current, thereby absorbing the light. The new layer may be the recording layer itself or a layer adjacent to the recording layer. Because a heat generates only from a small area of the optical disk at the time of recording, the disk can be turned rapidly and permissively to the auto focusing and tracking offsets, thereby enabling fast and high density recording. The disk can thus be formed with easily selectable multiple layers.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to media, methods, and apparatusesfor recording and reproducing information by means of light irradiationrespectively.

[0003] 2. Description of Related Art

[0004] The most significant features of optical disks are removabilityfrom their recording/reproducing apparatuses and availability with lowprices. Optical disk drives that use those disks are thereforeconfigured so as to enable fast and high density recording withoutlosing such the features of the optical disks.

[0005] So far, various well-known principles have been employed forthose optical disks; each records information in its recording layer byirradiating a light therein. One of such the principles makes good useof changes of atomic configuration caused by a thermal process, that is,phase-changes of a subject film material (the phase-change is alsoreferred to as phase transition or phase transformation) to enable theinformation recording medium made of the material to be rewritten manytimes. For example, a phase-change optical disk disclosed by JP-ANo.344807/2001 is basically configured by a protective layer, arecording film made of a GeSbTe material, a protective layer, and areflection layer, which are formed sequentially on a substrate.

[0006] On the other hand, there are also other well-known optical disksreferred to as electric-field-effect type disks. In the case of thistype disk, a laser beam is irradiated to its phase-change recording filmwhile an electric field is applied thereto so as to record informationtherein. This type disk has an element structure in which a phase-changerecording layer made of a GeSbTe material or the like is disposedbetween upper and lower electrodes. This electric-field-effect typeoptical disk is disclosed, for example, by JP-A No.122032/1988. Thistype optical disk receives an electric-field in its recording film,thereby the phase-change in the recording film is promoted(crystallization) more than other optical disks for each of which only alaser beam is irradiated to its recording film. FIG. 1 shows aconfiguration of such an electric-field-effect optical disk. A light 9is condensed by a lens 8. The disk has electrodes and layers formed on asubstrate 7 sequentially from the light incidence side in order of atransparent electrode 1, a UV-resin guide groove layer 2, a recordingfilm, an insulator electrode 4, an AI electrode 5, and a protectivelayer 6. A voltage is applied to both of the transparent electrode andthe AI electrode. The UV-resin layer 2 that has a guide groove on itssurface is an insulator whose specific resistance is 10 ⁶Ω.cm. TheUV-resin layer 2 functions as an electric-field-effect buffer layer andto form the guide groove.

[0007] A paper written by the present inventor et al (M. Terao, H.Yamamoto and E. Maruyama) and entitled as “Highly Sensitive AmorphousOptical Memory: supplement to the J. of the Japan Society of AppliedPhysics Vol. 42, pp233-238” reports an experimental result that lightirradiation to both of a light conductor and a phase-change recordingfilm disposed between transparent electrodes while a voltage is appliedto them from those transparent electrodes makes it possible to recordinformation in the recording layer only with a laser beam that is weakerby almost two digits than any case in which only a light is irradiatedthereto. On the other hand, there are also still other type opticaldisks like CR-R and DVD-R, each of which uses an organic-material forits recording layer. In the case of those optical disks, a laser beam isirradiated to both of a recording layer and a substrate surface adjacentto the recording layer. The recording layer includes a color matter tobe absorbed by the wavelength of the recording power supply, thereby thequality of the substrate surface is changed to enable information to berecorded therein.

[0008] As described above, while optical disks are all characterized byremovability from their recording units, as well as availability at lowprices realized by using plastic substrates, rapid operation is one ofthe indispensable requirements for them. And, because of such thestructure, optical disks have been confronted unavoidably with problems;each of those disks repeats pitching, resulting in tracking offsetssometimes when it rotates faster. And, this comes to generate a highfrequency that makes it difficult for the disk to follow up withauto-focusing and tracking. This is why the recording media have longbeen required to be permissive to such the tracking offset, especiallywhen in recording during which such the trouble is apt to occur. And,this conventional problem has to be solved to speed up the operation ofthe recording apparatus to enable such the following-up over themechanical vibration limit of the apparatus.

[0009] According to the technique disclosed in the above-described paper“supplement to the J. of the Japan Society of Applied Physics Vol.42”written by the present inventor et al, as well as theelectric-field-effect type recording medium disclosed by JP-ANo.122032/1988, it never occurs that only one of the land area and thegroove area becomes easier to be recorded, since almost the same voltageis applied to both of the areas and almost the same light absorptionoccurs in them. Consequently, the media in the above cases are notpermissive so much to the tracking offset and accordingly they cannotcope with fast recording satisfactorily. On the other hand, in the caseof the CD-R and the DVD-R, light absorption makes no differencepractically between the land area and the groove area, so that noelectric current application can assist the recording.

[0010] Under such circumstances, it is an object of the presentinvention to solve the above-described conventional problems and enablemass of information to be recorded stably and rapidly.

SUMMARY OF THE INVENTION

[0011] Hereunder, the configuration of the present invention for solvingthe above conventional problems will be described.

[0012] Note that, however, a long recessed portion formed on thesubstrate will be referred to as a groove in the present invention. Anarea between such grooves will be referred to as a land. Upon a lightincidence to a film through the substrate, such a groove looks like aconvex from the light incident side. Therefore, even in the case of themethod that applies a light from an opposite side of the substrate, sucha portion that looks like a convex at a view from the light incidentside might be referred to as a groove in some cases. This portion isrecognized as a convex when only the substrate is watched, but it isactually a land between grooves. Strictly, such a portion is notreferred to as a groove in the definition by the present invention. Inthe case of a method for recording information in either lands orgrooves, that is, in the case of the so-called in-groove recordingmethod, the recording characteristics are often better when in recordingat convex portions at a view from the light incident side regardless ofwhether the light incidence is done from the substrate side or from anopposite side of the substrate. However, those two methods are basicallysimilar to each other, so that recording may also be done at recessedportions at a view from the light incident side.

[0013] Concretely, the configuration of the present invention will be asfollows.

[0014] (1) A first electrode, an electro-chromic material, and a secondelectrode are disposed on a substrate of the information recordingmedium of the present invention, then a voltage is applied to betweenthe first and second electrodes to flow an electric current in theelectro-chromic material, which is thus colored. The informationrecording medium is preferably configured so that the electro-chromicmaterial is colored in a first area while it is not colored in a secondarea. The first area is equivalent to a land area and the second area isequivalent to a groove area. And, because the light is absorbed only inthe first area or in the second area, the easily recordable range can beidentified. Consequently, information can be recorded in the targetplace stably regardless of slight changes of the light spot and thelight condensing level, thereby the medium can record information fastand permissively to both AF and tracking offsets. The medium can alsocope with high density recording.

[0015]FIG. 2 shows a structure of the information recording medium ofthe present invention. In order to make it easier to understand, thestructure is illustrated so that a light is applied from the upper side.The medium is configured by layers and electrodes formed sequentiallyfrom the light incident side on a substrate 17 in order of a protectivelayer 11, a first electrode (transparent electrode) 12, anelectro-chromic material layer 13, a second electrode 14, a UV-resinlayer 14, and another protective layer 16. Other reference numerals aredefined as follows; 18 denotes a groove area and 19 denotes a land area.Another layer, which is, for example, a thin insulator layer or layerreferred to as a boundary layer may be formed between the recordinglayer (electro-chromic material layer) and the first or secondelectrode. The additional layer should preferably be 20 nm or under inthickness.

[0016] In another aspect, the information recording medium of thepresent invention is configured by a first electrode, an insulator filmhaving a through opening to the substrate, a recording film formed so asto be extended from the opening onto the insulator film and enabled torecord information therein, and a second electrode formed on therecording film. In this case, one of the land area and the groove areais formed as the opening of the insulator film and the insulator film isformed in the other. Consequently, only one of the groove and land areasbecomes the opening of the insulator film, so that the upper and lowerelectrodes come closer to each other. An electric current thus flowsbetween those electrodes. On the other hand, an insulator film is formedin the other (the land area or the groove area), so that no electriccurrent flows between those electrodes. This is why almost no currentflows between those electrodes. The current flowing range is thuslimited, thereby the easily recordable range is limited.

[0017] And, due to the features described above, the medium assuresstable recording regardless of slight changes of both light spot andlight condensing level, thereby enabling fast recording permissively toAF and tracking offsets. The medium can also cope with high densityrecording.

[0018] The present invention, therefore, intended to further improve therecording density, is also suited for multi-layer recording. Any of theconventional media has been required to form multiple layers to improvesuch the effective recording density (effective surface density). And,for a medium consisting of three or more layers, the transmission factorand the recording density comes into a trade-off relationship, andaccordingly either of the raw signal quality or the recordingsensitivity in each of the layers have been forced to be sacrificed. Inorder to solve such the problem, of the well-known three-dimensionalrecording methods uses the thickness direction of each subjecttransparent organic material for recording information. Another methodmakes good use of two-light-quantum absorption. The recordingsensitivity of this method, however, is very low and still anothermethod that employs light polymerization has a problem that both storagestability and recording sensitivity are low.

[0019] In the present invention, two or more recording layers are formedand each recording layer other than the farthest one from the lightincident side is disposed between transparent electrodes to improve thetransmission factor of each layer, thereby improving both recordingsensitivity and reproduced signal quality.

[0020] For multi-layer recording when the subject medium consists of twoor more recording layers, each of the recording layers other than thefarthest one from the light incident side, when information is to berecorded therein or to be read therefrom, should preferably be disposedbetween electrodes and the recording/reading laser beam absorptionfactor should increase upon applying of a voltage to between thoseelectrodes. The farthest recording layer from the light incident sidemay also be processed similarly. Therefore, every layer can be disposedin the focal depth of the focusing lens, since the layer is notinterfered by any other layers. The information recording medium canthus be provided with multiple layers and a large capacity than any ofthe conventional disks consisting of a plurality of layers respectively.To achieve this object, each recording layer or a layer adjacent to therecording layer may be a mixed material layer or stacked layer made ofan organic or non-organic electro-chromic material orelectro-luminescent material and a photo-chromic material. Consequently,the medium can be configured so that a light is absorbed in a givenlayer and almost not in other layers. It is also possible to disposesome of the layers out of the focal depth of the focusing lens and movethe focal point to record/read information in/from those layers, ofcourse. In this case, although a stacked layer consisting of many layersmight cause pits and grooves for representing address information to bedeformed, such the problem can be avoided by forming another layer inwhich those pits and grooves are copied so as to prepare for reading atleast address information from any one of the layers in the focal depthat the moved focal point. The above described electro-chromic materialmay be, for example, a polymer consisting of tungsten oxide andthiophene organic molecules.

[0021] Various other electro-chromic materials such as those describedin “Electro-chromic Display” issued by Sangyo Tosho (Co.) on Jun. 28,1991 and those described in papers at present are also usable.

[0022] A phase-change recording layer (ex., Ge₂Sb₂Te₅ layer) may bedisposed between the electro-chromic material layer and the first orsecond electrode. The layer should preferably be formed at the otherside of the light incidence from the optical point of view. In thisconnection, the electro-chromic layer should have a high recordingthreshold value and the phase-change recording layer should have a lowfusing point including that of such sulfur as Sb₄Te₃S₂ so thatinformation is recorded only in the phase-change recording layer or theelectro-chromic layer may be eliminated.

[0023] (2) As shown in FIG. 3, a photo-conductor layer 23 may be formedbetween the first or second electrode 22 and the recording film 24. Thephoto-conductor layer 23 should be formed closer to the light incidentside electrode than the recording film. In this connection,photo-carriers generated in the photo-conductor layer 23 due to thelight irradiation are moved, thereby the resistance of thephoto-conductor layer 23 lowers and both voltage and electric currentapplied to the recording layer 24 comes to increase sharply. As aresult, the temperature of the light irradiated portion of the recordinglayer rises. The recording layer is thus enabled for recording. Thephoto-carriers may also increases through the avalanche multiplicationeffect. A photo-conductor film formed such way has a high densityelectric current flown in the recording film, thereby the lightincidence energy is reduced. The electro-chromic material layer may alsobe used as a photo-conductor layer.

[0024] The recording layer may also be used as a photo-conductor layeror the recording layer may be of a type in which the electric resistancemay drop upon rising of the temperature of the layer. Such achalcogenide material as Ge—Sb—Te or the like, such an organic conductormaterial as polythiophene or the like are equivalent to the layer ofwhich electric resistance drops due to a temperature rise in the layer.In FIG. 2, reference numerals are defined as follows; 21 denotes aprotective layer, 22 denotes a transparent electrode, 25 denotes aninsulator layer, 26 denotes a second electrode, and 27 denotes aprotective substrate. The UV-adhesive layer is omitted here.

[0025] (3) A circular information recording medium may be used andprovided with a third electrode that is long in the radial direction ofthe medium used to supply an electric current to the first and secondelectrodes. The third electrode can apply the same voltage up to theouter periphery of the medium.

[0026] (4) The voltage application to between the first and secondelectrodes during light irradiation should preferably be done after thelight irradiation. When a light is irradiated to between the first andsecond electrodes concurrently with a voltage, the electric currentincreases around the light irradiated portion as shown in FIG. 8. And,if the voltage is kept applied thereto even after the end of the lightirradiation, the resistance in the portion rises due to any of thereduction of excitation carriers, the fusion of the recording filmitself, the disarray/resolution of the atom/molecule configuration,thereby the electric current flow in the layer decreases automatically.After the current returns to its initial value, the state of therecording layer changes. For a disk-like medium, therefore, thepowering/heating time for recording becomes almost the same at bothinner periphery and outer periphery. Thus, the method will also beadaptable easily for the CAV (Constant Angular Velocity) recording. And,the electric current that flows throughout the recording medium growsinto a large current, thereby preventing occurrence of insufficientsupply of the current, state changes of the recording film, andexcessive expansion of damaged areas. In order to achieve this object,the recording apparatus is just provided with a control circuit forsuppressing the voltage application under 80% of that for enablingrecording.

[0027] (5) One of the first and second electrodes should preferably bedivided into a plurality of electrodes. If such an electrode is dividedin the radial direction, the medium will also be suited for the CAV(Constant Angular Velocity) recording and the capacitance betweenelectrodes can be reduced to improve the response speed.

[0028] (7) When in recording, the recording laser power can be set atover 0.2 mW to 2 mW (excl.) even at a linear recording speed of 15 m/sor over. If the recording sensitivity is such improved, a highertransfer rate can be achieved without causing insufficient laser powerapplication even for high linear speed recording when an arraylaser/surface emission laser is used for simultaneous light irradiationon a plurality of spots on the medium. In this connection, it is alsorecommended to make pulse-like light irradiation also in erasure areasand set a pulse width wider than that of the recording mark formingpulses. Consequently, rewriting is enabled satisfactorily while it isavoided to widen the erasing width excessively. A voltage may also beapplied simultaneously to at least the plurality of electrode pairs onthe recording medium in units of two pairs. This method is necessarywhen a low material maintenance voltage is applied to cause the materialcolor to be changed.

[0029] The recording medium of the present invention may also beprovided with a plurality of recording layers and a voltage is appliedto between those pairs of electrodes while a different voltage isapplied to between electrodes disposed only at both sides of a targetlayer when in recording, erasing, or reading.

[0030] (8) In order to achieve the above object, the recording apparatusof the present invention is provided with two means; one means forpositioning a plurality of electrodes disposed at a portion where therotary shaft of the disk motor or the disk receiving part attached tothe rotary shaft comes in contact with the center hole of the disk sothat each of the plurality of electrodes faces each of the predeterminedelectrodes disposed in the center hole of the disk when the disk isloaded and the other means for making each electrode disposed at therotary shaft side contact with each electrode disposed at the disk side.Consequently, a predetermined voltage comes to be applied to eachelectrode.

[0031] In another aspect, the information recording apparatus of thepresent invention is provided with a tapered projection in the verticaldirection at least at one place in the circumferential direction of aside surface of the disk motor rotary axis or disk receiving partattached to the rotary shaft. The disk is provided with a plurality ofdivided electrodes at a portion having a height, where the disk is to beloaded. Consequently, the disk is positioned accurately in the turningdirection, thereby a power is supplied accurately to each of theelectrodes disposed in the multiple layers.

[0032] The present invention is thus effective for the recording density(track pitch, bit pitch) over the 2.6 GB DVD-RAM standard and moreeffective for the recording density over the 4.7 GB DVD-RAM standard.When the light source wavelength is not around 660 nm and when thenumerical aperture (NA) of the focusing lens is not 0.6, the presentinvention is effective for the recording density over a value calculatedon those conditions in terms of wavelength ratio or NA ratio in both ofthe radial direction and the circumferential direction.

[0033] In this specification, a term “phase-change” is used and the“phase-change” includes not only the phase-change between crystal andnon-crystal, but also the phase-change between fusion (change to theliquid phase) and re-crystallization, as well as the phase-changebetween crystal states.

[0034] In this specification, the present invention premises that theelectro-chromic material layer mentioned above means a layer made of amaterial that develops its color directly (due to a light absorptionspectrum change) by an applied voltage defined ordinarily, as well as alayer including an area that emits a light due to an applied voltage (aflown electric current) and an area that develops its color ordistinguishes its color with a light received from the light emittingarea.

[0035] Furthermore, “the electro-chromic material of the presentinvention is conductive” is defined as a constant flow of an electriccurrent of 0.1 mA or over when 2 V is applied to between the first andsecond electrodes of a disk whose diameter is 80 mm or over.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a structure of a conventional information recordingmedium;

[0037]FIG. 2 is a cross sectional view of an information recordingmedium in an embodiment of the present invention;

[0038]FIG. 3 is another cross sectional view of the informationrecording medium in another embodiment of the present invention;

[0039]FIG. 4 is a ¼ view of the information recording medium in theembodiment of the present invention;

[0040]FIG. 5 is a bird's-eye view of part of the information recordingmedium in the embodiment of the present invention;

[0041]FIG. 6 is a cross sectional view of the recording medium to besubjected to an etching process for exposing an insulator layer thereofin the embodiment of the present invention;

[0042]FIG. 7 is an electrode disposed in part of a disk holder in whichthe information recording medium in the embodiment of the presentinvention is to be loaded;

[0043]FIG. 8 is a chart for denoting changes of a current with time,which flows in one recording spot of the information recording medium ofthe present invention;

[0044]FIG. 9 is a block diagram of the information recording medium ofthe present invention;

[0045]FIG. 10 is a chart for describing a relationship between a ratioof the distance between electrodes and a drop of a signal level due to atracking offset;

[0046]FIG. 11 is a structure of a stacked layer of a multi-layer disk ofthe present invention;

[0047]FIG. 12 is a molecule structure in an organic electro-chromicmaterial;

[0048]FIG. 13 is another molecule structure in an organic photo-chromicmaterial;

[0049]FIG. 14 is a structure of the information recording medium and anoptical system in the embodiment of the present invention;

[0050]FIG. 15 is a block diagram of an applied voltage reversing andcontrolling circuit in the embodiment of the present invention; and

[0051]FIG. 16 is part of an electrode in a disk holder in which theinformation recording medium in the embodiment of the present inventionis to be loaded.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] <First Embodiment>

[0053] (Structure and Fabrication Method)

[0054]FIGS. 4 and 5 show structures of a disk-like information recordingmedium in the first embodiment of the present invention. FIG. 4 shows a¼ size view of the structure of the disk and FIG. 5 shows an expandedview of the ¼ size portion of the disk. In FIG. 4, only two upperradial-patterned transparent electrodes are shown while many more aredisposed actually all over the disk surface. A light forrecording/reading is irradiated from above through the substrate whilethe top substrate is not shown in FIG. 4. FIG. 5 shows an expanded viewof part of the disk. Also in FIG. 5, the top substrate and the insulatorlayer are not shown so as to simplify the description. In FIG. 5,reference numerals are defined as follows; 45 denotes a reflectionelectrode, 43 denotes a recording layer, 44 denotes an insulator layer,42 denotes a photo-conductor layer, 41 denotes a transparent electrode,46 and 50 denote light spots, 47 denotes a groove area, and 48 denotes aland area. Usually, information is recorded/read in/from portionsreferred as to groove areas, which look like convex portions at a viewfrom the light spot. In this embodiment, however, information isrecorded in land areas. The notches shown beforehand in FIG. 5 are partof the A-A′ cross section and the upper notches shown in FIG. 5correspond to gaps between radial patterned electrodes shown in FIG. 4.The entire A-A′ cross sectional view becomes as shown in FIG. 3.

[0055] This recording medium is fabricated as follows. At first, asshown in FIG. 6, a tracking groove (width: 0.25 micron) is formed on apolycarbonate substrate 57. The groove is used for in-groove recording(recording in the land area at a view from the light spot here) at0.45-micron track pitches at a diameter of 12 cm and a thickness of 0.6mm. Addresses are represented by the groove wobbling on the substrate.On the substrate are also formed transparent electrodes (ITO) made of(In₂O₃)₉₀(SnO₂)₁₀ at a film thickness of 30 nm. A groove pattern is thencopied onto the surface of the substrate with use of a mother to whichthe pattern is copied once from a nickel master formed by plating thephoto resist of the original disk. This is to correspond the exposedphoto-resist of the groove to the land. FIG. 6 shows processes forforming the films on the substrate 57. Note that the structures shown inFIGS. 4 and 5 are upside down in FIG. 6. Then, an As₃Se₉₇ layer 52,which is a photo-conductor layer, is formed at a thickness of 50 nm.After this, a Ge—Sb—Te recording layer 54 is formed at an average filmthickness of 10 nm. This transparent electrode layer is formed by meansof spattering through a mask, thereby the electrode is isolated in theradial pattern area 20 corresponding to the recording sector. Then, aSiO₂ layer, which is an insulator layer 55, is formed at a thickness of120 nm. It is followed by forming an acrylic-resin layer 56 at anaverage thickness of 25 nm as shown at the top in FIG. 6. A ultra-violetlight having a wavelength of 254 nm is applied to the layer 56 to etchuntil the relatively thin resin layer is removed from the land area.This is followed by performing reactive ion etching for the layer 56 toremove the SiO₂ layer from the land area, thereby the recording layer 53is exposed. In other words, a through-opening to the insulator layer isformed. Such the method in which the film thickness of a layer ischanged between the land and the groove to improve the recordingsensitivity in one of the land and the groove, thereby increasing thepermissiveness to both tracking and auto-focusing offsets is alsoeffective for recording media to which only a light is applied to recordinformation (while no voltage is applied). After this, the acrylic resinis almost completely removed from the substrate surface by means ofplasma asher. As a result, the information recording medium in thisembodiment comes to be structured as shown in FIG. 3. In the case of therecording medium in this embodiment, the total film thickness at eachportion between electrodes depends significantly on whether or not aninsulator film exists there; the film thickness differs by twice or morebetween existence and non-existence of the insulator film. And, becausethe resistance of the SiO₂ layer is larger than those of other layers,the resistance of every layer between electrodes takes a ratio of 1:2 orover between the through-opening and each of other portions. When therecording layer is a phase-change recording layer, any of such theGe—Sb—Te recording materials as known Ge₂Sb₂Te₂, Ge₅Sb₇₀Te₂₅, etc, aswell as an Ag—ln—Sb—Te recording materials is usable. The recordinglayer may also be made of an electro-chromic material such aspolythiophene to be described in detail in the second embodiment. Next,a W₈₀Ti₂₀ film is formed at a thickness of 50 nm. The film is used asboth of a reflection layer and a second electrode layer 45. A magnetronspattering apparatus is used for forming the stacked film.

[0056] Voltage application to the outer periphery of the disk mightoften be disturbed by the transparent electrode sheet resistance and thethinner portions of the transparent electrodes formed at angles ofconvex and concave portions of the groove. And, to avoid this problem,one or two thin metallic (AI or Ag is recommended) electrodes 39/40should preferably be formed on the substrate before the transparentelectrodes are formed on the substrate. The electrode 39/40, which isnarrower than the radial patterned transparent electrode, is a thinmetallic electrode extended from the inner periphery to the outerperiphery of the disk and about 100 microns in average width in theradial direction and 50 nm to 200 nm in film thickness. These metallicelectrodes are formed on the medium by means of spattering through amask. These electrodes are avoided when in recording/reading.

[0057] Unlike the above embodiment, when information is to be recordedin a portion that looks like a groove at a view from the light spot, itis just required that the transparent electrode layer and the reflection& electrode layer are replaced with each other and the light isirradiated from the protective substrate side. In this case, the nickelmaster is used to form the substrate, not the mother one. The protectivesubstrate may be thinned to about 0.1 mm and the NA of the focusing lensmay be increased to 0.85. As a result, the track pitch can be narrowedto about 0.33 micron, which is about ¾ of that in the above embodiment.

[0058] Although a photo-conductor layer is employed in this example, ifthe recording film is also used as a photo-conductor layer, there is noneed to form the above-described photo-conductor layer; for example,only an electro-chromic material layer or phase-change recording layermay be formed between electrodes. In such a case, the insulator layercan be omitted, so that the cross sectional view of the recording mediumbecomes as shown in FIG. 2. The electro-chromic material layer will bedescribed in detail in the second embodiment. In this embodiment, athiophene derivative material is used. Other materials to be describedin the second embodiment are also usable, of course. The electro-chromicmaterial layer, as to be described in detail in the second embodiment,consists of three layers, which are formed by means of coating, vacuumdeposition, or electrical field polymerization. The polymer layer of thethree layers is formed by means of coating, so that the film thicknessis thin in the land area and thick in the groove area on the substrateas shown in FIG. 2. The electro-chromic material layer develops itscolor when a voltage is applied to between the transparent electrodelayer and the electrode layer. However, because the distance betweenelectrodes in the land area is shorter, the land area develops its colorearlier. If the land area develops its color due to a voltage appliedthereto as described above and the voltage application stops or it iscontrolled low while the groove area does not develop its color enoughto suppress or keep the color development, then recording and readingare done accurately even upon occurrence of a tracking offset caused bythe faster rotation of the disk during recording/reading. This isbecause the light absorption becomes higher only in the land area.

[0059] A very thin conductor layer (metallic layer or transparentelectrode layer) should preferably be formed between a recording layerand a photo-conductor layer so as to suppress mutualdispersion/reaction. If the layer is formed, the reliability of themedium will increase more when in repetitive rewriting. In this case,however, the film thickness should be 1 nm or over and 10 nm or under sothat the photo-carrier generated in the photo-conductor layer breaksthrough the layer. The film may be a band-like or reticulatediscontinuous film. For example, if a 5 nm thick W₈₀Ti₂₀ electrode layeris formed between the recording layer and the photo-conductor layer, thesurface potential can be set in uniform, mutual dispersion between therecording layer and the photo-conductor layer can be prevented duringrewriting, thereby the number of rewriting times is improved by a singledigit.

[0060] A plurality of radial pattern transparent electrodes may bereplaced with one electrode formed all over the disk surface. However,when the plurality of radial pattern electrodes are used, thecapacitance between electrodes becomes smaller, thereby the voltagesupply can start and stop quickly. The capacitance between electrodesshould preferably be 0.1 F or under, since both time and electriccurrent required for coloring/decoloring are within a predeterminedrange. The recording medium should be structured so as to control thecapacitance between electrodes to 0.1 F or under to keep the goodcharacteristics of the elements. Instead of dividing the transparentelectrode, the metallic electrode may be divided or both of the upperand lower electrodes may be divided. If an electrode is divided suchway, whether or not the breaks of the divided upper and lower electrodesare aligned is no matter.

[0061] A leader electrode is formed at the innermost periphery of eachof the reflection layer & electrodes and the above transparentelectrodes. This leader electrode reaches the innermost periphery of thedisk and is connected to corresponding one of a plurality of electrodes35 and 36 disposed at the end face of the disk's center hole so that itis connected to another electrode on the disk rotary shaft of therecording/reading apparatus as shown in FIG. 4. As shown in FIG. 7, sixelectrodes are bonded separately (only three 65 to 67 of the sixelectrodes are shown in FIG. 7) at a portion having a height, where thedisk is to be loaded on the side of the rotary shaft 61 of the diskmotor through which the disk receiving disc 68 is extended. At one placein the circumferential direction of the rotary shaft is formed a taperedprojection 70 or a concave in the vertical direction, which is fit by aconcave or convex formed in the disk's center hole to position the disk,thereby predetermined electrodes come in contact with each other. Eachelectrode of the disk's rotary shaft receives a power supplied from thecircuit substrate of the recording apparatus generated by a combinationof a plurality of brushes and rings 62 to 54. The power supply methodmay be replaced with another. For example, instead of the brushes andrings (slip rings), a non-contact method or the like may be employed.The non-contact method combines a rotary connector in which a tip of acontact put in a mercury tank is rotated, laser, or LED with a solarbattery. The rotary connector is available on the market.

[0062] A UV-curing resin is coated on the film surface of theabove-described disk member, then stacked on another same shapesubstrate to complete the disk-like information recording medium of thepresent invention.

[0063] The laser beam for recording/reading is irradiated on the mediumfrom the substrate side. The transparent electrode layer formed on themedium last may be used as a transparent electrode layer so as toirradiate the laser beam on the medium from the protective substrateside. In this case, the thickness of the recording film is decided sothat the reflection rate becomes about 10% to satisfy a required readcontrast ratio.

[0064] [Initial Crystallization]

[0065] The phase-change recording layer of the disk fabricated asdescribed above is crystallized in the initial stage as follows. Thedisk is turned and a laser beam having a power of 800 mW is applied tothe recording layer 24 through the substrate 28. The laser beam spot ofthe semiconductor laser (wavelength: approx. 810 nm) is elliptic long inthe radial direction of the medium. The laser beam spot is then movedstep by step in units of ¼ of the spot length in the radial direction ofthe medium. The medium is thus crystallized in the initial stage. Thisinitial crystallization may be done only once. When this crystallizationis done twice, the noise to be caused by crystallization is a littlesuppressed.

[0066] (Recording, Erasing, and Reading)

[0067] Information is recorded/read in/from the above-describedrecording medium as follows. Hereinafter, how the recording/reading isdone will be described with reference to FIG. 9. The ZCAV (ZonedConstant Linear Velocity) method is employed for controlling the motorto change the rotation speed of the disk in each zone forrecording/reading.

[0068] Information from external is received in units of 8 bits andtransferred to an 8-16 modulator 8-8. When information is to be recordedon the information recording medium (hereinafter, to be referred to asthe optical disk) 8-1, a so-called 8-16 modulation method is used toconvert 8-bit information to 16-bit information. This modulation methodrecords information having a 3 T to 14 T mark length corresponding to8-bit information. The 8-16 modulator 8-8 in FIG. 9 performs such themodulation. The “T” mentioned above means a clock cycle at the time ofrecording. The optical disk is turned so that the relative speed withrespect to each light spot becomes a linear speed of 15 m/s.

[0069] The 3 T to 14 T digital signals converted by the 8-16 modulator8-8 are transferred to a recording waveform generator 8-6, so that amulti-pulse recording waveform is generated there.

[0070] At this time, the power level for forming recording marks is setat 5 mW, an intermediate power level for erasing the recording marks isset at 2 mW, and a reduction power level is set at 0.1 mW respectively.The laser power for forming recording marks can be lowered in responseto the rising of the applied voltage. The recording is donesatisfactorily within a range over 0.5 mW to 5 mW. No significant changeappeared within the range even when the linear speed is changed toanother from 15 m/s. Reading from the medium is done at 1 mW with novoltage application. Reading is practically possible within a range over0.2 mW to 2 mW. When in reading at a power level over 2 mW for a longtime, recorded data is degraded. In the above-described recordingwaveform generator, 3 T to 14 T signals are corresponded to “0” and “1”alternately in a time series. At this time, non-crystallization occursin each area (mark area) in which high power level pulses are applied.The recording waveform generator 8-6 has a multi-pulse waveform tablecorresponding to a method (adaptive recording waveform control) forchanging the pulse widths of both leading and trailing pulses of themulti-pulse waveform in correspondence with the length of each spacebefore and after each mark area. The recording waveform generator 8-6thus uses the table to generate multi-pulse recording waveforms free ofthe thermal interference that might occur between recording marks.

[0071] The recording waveform generated by the recording waveformgenerator 8-6 is transferred to a laser driver circuit 8-7 and the laserdriver circuit 8-7 emits a light of the semiconductor laser disposed inthe optical head 8-3 according to this recording waveform.

[0072] The optical head 8-3 installed in this recording apparatus uses asemiconductor laser having a light wavelength of 400 nm used forrecording information. The objective lens having a lens NA of 0.65focuses this laser beam on the recording layer of the optical disk 8-1to apply the laser beam to the target area so as to record informationtherein.

[0073] In the phase-change recording layer, the reflection rate of themedium becomes higher in the crystal state than that in the non-crystalstate which is set after information is recorded therein. Whileinformation is recorded by means of laser beam irradiation, a 5 Vvoltage is applied continuously to between upper and lower electrodes ofthe recording layer. And, photo-carriers (electrons, pairs of positiveholes) are generated in the Se-As layer, which is a photo-conductorlayer, due to the irradiated pulse laser beam, thereby the electricresistance lowers. As a result, the voltage applied to this portion inthe recording layer rises, thereby an electric current path is formed inthe recording layer. In addition, an area is formed in the recordinglayer. In the area, the fusing point is exceeded by the Joule heat ofthe electric current. After this fusing, the electric resistance in thisarea rises, thereby the electric current path disappears and the areacools down to become non-crystallized. Consequently, both deflectionrate and extinction coefficient are changed, thereby signals can be readfrom this area optically. By repeating the irradiation of this pulselaser beam according to information signals, non-crystal recording markstrings are formed. When the recording is speeded up, the laser beampoint is moved fast and the electric current keeps flowing until therecording layer is fused and the electric resistance in the area riseseven after the laser beam irradiation as shown in FIG. 8 (electriccurrent changes with time). The electric current thus flows in aplurality of places simultaneously, then the current stops sequentiallyin order of current application start.

[0074] Because the recording is done in such the mechanism, the currentflowing time is almost fixed regardless of the radius of the disk,although the laser spot passing time depends on the radius of therecording track. It is therefore easy to record information at a fixedration speed (CAV) that is difficult on ordinary phase-change opticaldisks. A voltage is applied sequentially to each of the plurality ofdivided transparent electrodes in each laser-beam-irradiated area.

[0075] Because of the high recording sensitivity, the above recordingmedium enables recording to be made in a plurality of laser spotssimultaneously. In addition, because the light absorption is notrequired so much, both high reflectivity and high transmittance areobtained for recording and a high S/N ratio is assumed for reading. Whenvoltage application is suppressed upon reading, a high laser power isassumed for reading, thereby a high S/N ratio is obtained.

[0076] The recording medium in this embodiment is structured so thatupper and lower electrodes are disposed closely to each other only inthe groove area. A high electric field is thus applied just in a narrowrange in the recording film. Consequently, stable information recordingis assured regardless of slight changes of the laser spot and/or thelight condensing level, thereby the recording medium becomes permissiveto the AF and tracking offsets, sensitive to a light, and suited forrecording at a fast rotation of the medium.

[0077] The recording medium in this embodiment can also obtain a lightreflection contrast ratio of about 2:1 between recording marks and otherportions. When the contrast ratio lowers, the fluctuation of readsignals to be caused by noise exceeds 9% of the upper limit, therebypractical read signal quality comes to exceed the limit. To avoid thisproblem, SiO₂ is included in the transparent electrode layer to form a(SiO₂)₄₀(In₂O₃)₅₅(SnO₂) layer. As a result, the reflection rate lowersto improve the contrast ratio to 2.5:1 or over.

[0078] Because of the recording principles as described above, aplurality of laser beam spots are formed in the same recording track ordifferent recording tracks with use of a single or a plurality ofoptical heads, thereby information is recorded easily in the track(s)simultaneously.

[0079] When in erasing, an applied voltage is lowered and the laser beamis applied continuously to the target non-crystal area to crystallizethe area. A pulse laser beam may be used for this erasing and the laserbeam pulse may be wider than any of the recording pulses.

[0080] The recording apparatus of the present invention can employ amethod for recording information in the land area (a variation of theso-called in-groove recording method).

[0081] The above optical head(s) are also used for reading recordedinformation. Concretely, a laser beam is irradiated on each recordedmark and reflected beams from the mark and another portion are detectedto obtain a read signal. The amplitude of this signal is amplified by apreamplifier circuit, then converted to 8-bit information by an 8-16demodulator 8-10 in units of 16 bits. This completes the reading of therecorded marks.

[0082] When in recording with use of mark edges under the aboveconditions, the shortest mark 3 T becomes about 0.20 μm and the longestmark T14 becomes about 1.96 μm in length respectively. Each recordsignal includes dummy data in both start and end parts respectively; inthe dummy data, a 4 T mark and a 4 T space are alternated and the startpart also includes a VFO.

[0083] (Mark Edge Recording)

[0084] The mark edge recording method is employed for high densityrecording in DVD-RAM and DVD-RW. This mark edge recording makes bothedges of each recording mark formed on the subject recording filmcorrespond to “1” of digital data, thereby the length of the shortestrecording mark can be corresponded to 2 to 3 reference clock pulses soas to realize high density recording. The DVD-RAM employs the 8-16modulation method and extends the length of the shortest recording markto three reference clock pulses. When compared with the mark positionrecording method that makes the center of each circular recording markto “1” of digital data, the mark edge recording method is moreeffective, since it realizes high density recording without reducing therecording marks so much in size. In spite of this, it is required thatshape distortion of recording marks must be minimized for the recordingmedia that employ this mark edge recording method.

[0085] (ZCLV Recording Method and CAV Recording Method)

[0086] Phase-change recording media, when the recording waveform remainsthe same, should preferably be enabled to record information at anoptimal linear speed corresponding to the crystallization speed toobtain satisfactory recording/reading characteristics. When accessing aspace between recording tracks that are different from each other inradius on a disk, it takes much time to change the disk rotation speedso as to equalize the linear speed between those tracks. In order tosolve this problem, the DVD-RAM employs the ZCLV (Zoned Constant LinearVelocity) method, which divides the disk surface into 24 zones in theradial direction, fixes the disk rotation speed in each zone, andchanges the disk rotation speed only when a zone to access must bechanged to another. According to this method, the linear speed differsslightly between the innermost track and the outermost track in eachzone, so that the recording density also comes to differ between thosetracks. Nevertheless, the method makes it possible to record informationalmost at the maximum density all over the disk.

[0087] On the other hand, the CAV recording method that keeps a fixeddisk rotation speed is suited for recording in which the disk rotationis kept as a fixed speed even upon an access to be made by skipping afar distance in the radius direction. This method is also suited formobile devices that can suppress the power consumption required forchanging the disk rotation speed. As described above, because thepresent invention also makes it possible to keep a fixed heating timeregardless of the position in the radial direction of the disk, it makesthe CAV recording easier.

[0088] The present invention also considers preventing ofre-crystallization as important. This is because the temperature inadjacent tracks is apt to rise when re-crystallization occurs inperipheral areas of a recording film that is fused due to the recordingtherein, thereby remaining non-crystallized recording mark area isnarrowed and a wider area must be fused to form recording marks in apredetermined size. The present invention can also prevent such there-crystallization, since the heat conductivity of the transparentelectrodes is low, so that the heat dispersion towards the innerperiphery of the disk is not so much. The present invention also makesit possible to prevent a problem that the heat in the center of eachrecording mark is diffused in the transverse direction and theperipheral area of the fused area cools down slowly, thereby there-crystallization that is apt to occur around there is suppressed.

[0089] (Tracking Margin)

[0090] In this embodiment, the upper electrode is in direct contact withthe recording film in the land area and an SiO₂ layer that is aninsulator layer is disposed between the upper electrode and therecording film in the groove area. Therefore, the electrode distanceratio between the land area and the groove area is 60:180, that is, 1:3.Usually, a tracking offset occurs due to the decentering of theinner/outer diameter of the disk and the offset occurrence increases inproportion to the disk rotation speed. The present invention, however,has successfully reduced such the offset occurrence during recording,since the recording medium is structured so that both electrode layerand recording layer come in contact with each other only in the landarea or color development occurs and the heat generation increasestherein. When a boundary layer is formed between an electrode and arecording layer, the electrode distance ratio between the land area andthe groove area becomes 65:145 if the boundary layer is 5 nm inthickness. If a tracking offset exceeds {fraction (1/10)} of the trackpitch, which is the normal upper limit, the distance ratio comes to havea relationship with a cross erasure event in which data is erased frompart of a recorded area in an adjacent track, thereby the signal leveldrops. The relationship becomes as shown in FIG. 10. Electrode distanceratio Signal level drop 1:3 −0.1 dB 1:1.5 −0.5 dB 1:1.4 −1 dB   1:1.3 −2dB   1:1.1 −3 dB   1:1.05 −4 dB  

[0091] As shown above, the distance ratio should preferably be 1:1.1 orover, and more preferably it should be 1:1.4 or over. The same effect isalso obtained from another recording method in which only a high powerlaser beam is irradiated on the target; no voltage is applied.

[0092] (Recording Layer)

[0093] Various recording layer materials are usable in accordance withthe required recording speed and other characteristics, for example,those employed for optical disks. Other usable materials are Ge—Sb—Tematerials, each consisting of Ge₂Sb₂Te₅, Ge₄Sb₂Te₇, or Ge₅Sb₇₀Te₂₅,Ag—In—Sb—Te materials consisting of Ag₄In₆Sb₆₅Te₂₅, etc. Although thosematerials disable phase-changes and frequently rewriting employed asrecording functions, those disabled functions may be realized by otherfunctions such as forming of holes in the recording layer(electro-chromic material layer, phase-change material layer, etc.)itself, color development capability break-down, color changes, as wellas changes and transformation of adjacent photo-conductor layer andsubstrate.

[0094] Organic materials are also usable in the case where rewriting isnot required so frequently. And, other various types of organicconductor materials to be described in detail in the second embodiment,as well as coloring matters whose conductivity is not so high,photo-chromic coloring matters, and other known coloring matters usedfor CD-R and DVD-R are also usable. When any of those coloring mattersis used, the recording mechanism to be employed will become opticalchanges or hole forming to be caused by structure changes of the subjectorganic material itself and/or photo-conductor layer and/or thesubstrate surface to occur due to the action of the laser beam and/orelectric current. For a material whose conductivity is not so high, thefilm should be as thinned as possible as long as the film is not eateninto conspicuous holes from the beginning.

[0095] (Photo-conductor Layer)

[0096] Because the substrate is subjected to a high temperature thermalprocess, the substrate material is limited. However, in addition to theabove As—Se materials, such known non-organic photo-conductor materialsas CdTe, CdS, CdSe, etc., as well as such organic conductor materials aspolythiophene, etc. to be described in detail in the second embodimentare usable as the colored photo-conductor material described above.

[0097] (Boundary Layer)

[0098] A boundary layer should preferably be disposed between arecording layer and an electrode to speed up both crystal core formingand crystal growing, thereby speeding up the crystallization. As suchthe boundary layer material, a group consisting of the following shouldpreferably be used. Concretely, the group consists of such a Ta oxide asTa₂O₅, such a Cr oxides as Cr₂O₃, such an AI oxide as Al₂₃, such an Sioxide as SiO₂, such a Ge oxide as GeO₂, such an Sn oxide as SnO₂, such aZr oxide as ZrO₂, such an oxide as Co and Ni, a single nitride or acompound of two or more of nitrides of Cr, Ge, Ti, Al, Si, Ta, Zr, B,and Hf. Among those, Cr₂O₃ is more preferable, since it can suppress thereflectivity fluctuation in frequently rewriting to 5% or under andreduce the jittering. CoO, Cr₂O, and NiO are also more preferable, sincethe crystal grains become uniform in diameter in the initialcrystallization, thereby the rising of the jittering can be suppressedin the initial stage of rewriting. AlN, TaN, TiN, ZrN, BN, CrN, Cr₂N,GeN, HfN, or Si₃N₄, Al—Si—N materials (ex., AlSiN2), Al—Ti—N materials,Si—Ti—N materials, Si—O—N materials, and a compound of those nitridesare also preferable, since the adhesive power becomes stronger and theinformation recording medium is less degraded by external shocks. Inaddition, such a Cr—Ge material as Cr80Ge20, a material that includes 60mol % or more of an oxide or nitride consisting of Cr and Ge willimprove the recording medium storage life and keep the high performanceeven under high temperature and high humidity.

[0099] (Materials of Electrodes)

[0100] A preferable electrode material depends on the utilization. Whenrewriting is to be done frequently, the material should be tungsten ormolybdenum, or a material that includes at least either of them andanother metallic element such as titanium or the like by less than 50atomic %.

[0101] On the other hand, when recording is to be done just once, thatis, recording or rewriting from/in a draw-type optical disk is to bedone so frequently, a metal suited for optical disks because of itsoptical characteristics and thermal diffusivity should be used forelectrodes. A metallic layer whose reflectivity and thermal conductivityare high, when it is Al or an Al alloy, should be a high thermalconductivity material that includes such additive elements as Cr, Ti,etc. by 4 atomic % or under, since it is effective to prevent thetemperature on the substrate surface from rising. In addition, thefollowing are also usable; a single element of Au, Ag, Cu, Ni, Fe, Co,CR, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, and V, or any of theAu alloy, the Ag alloy, the Cu alloy, the Pd alloy, and the Pt alloy,any of Sb—Bi, SUS, and Ni—Cr, or an alloymainly consisting of thoseelements, or an alloy consisting of those elements equally. The layerused as both an electrode layer and a reflection layer consists of ametallic element, a half-metallic element, an alloy of those elements,or a compound of those elements as described above. Among them, a singleelement of Cu, Ag, and Au, or any of the Cu alloy, the Ag alloy,especially, a material that includes such additive elements as Pd, Cu,etc. by 8 atomic % or under, a material such as an Au alloy whosethermal conductivity is high, since they can suppress the thermaldegradation of the organic materials. For the transparent electrodematerial, the following known materials are usable; a materialconsisting of (In23)×(SnO2)1−x (x: 5% to 99%), more preferably from thestandpoint of resistance, a material that includes 90% to 98% of the x,a material to which SiO2 whose mol % is 50% or under is added, amaterial obtained by adding another oxide such as Sb2O3 whose mol is 2to 5% to SnO2, as well as any of such conductor organic materials aspolythiophene, polyacethylene, etc.

[0102] (Insulator Layer)

[0103] The fusing point of an insulator layer around a recording layershould preferably be 600° C. or over. When a material whose fusing pointis lower than 600° C. is used for the insulator layer, the insulatorlayer will be degraded due to the heat generated in the recording layeror in the insulator layer itself when in recording and the opticalcharacteristics might be changed, thereby the S/N ratio lowers. Such therecording/reading characteristics are improved when the thickness andmaterial of each of the above layers are decided within the preferablerange with respect to each of the above items. Those preferable rangescan also be combined to further improve the recording/readingcharacteristics of the media. And usable insulator layer materials are asingle element of SiO₂, Al₂O₃, Cr₂O₃, Ta₂O₅, GeO₂, GeN, and Si₃N₄, anyof oxides and nitrides in which the composition ratio of those elementsis different from each other. Insulating organic materials are alsousable.

[0104] When an organic material is used to form an insulator layer, aphoto-conductor layer, and a recording layer by means of vacuumdepositing, especially by means of coating, the distance betweenelectrodes comes to differ naturally between the land area and thegroove area when the insulator layer is formed; there is no need to useother processes for generating a difference in film thickness betweenthose land and groove areas. The electric current can thus beconcentrated effectively in the layer.

[0105] (Substrate)

[0106] In this embodiment, a polycarbonate substrate 77 is used. Thesubstrate 77 has a tracking groove formed directly on its surface. Asubstrate having such a tracking groove comes to be a substrate that hasa groove of λ/15 n or over (n: refractivity of the substrate) entirelyon the surface or part of the surface when the recording/readingwavelength is assumed to be λ. The groove may be continuous ordiscontinued in one round. When the groove is about λ/12 n in depth, thebalance between tracking and noise is found to become satisfactory. Thegroove width may differ among places. The substrate may be formatted soas to record/read information in/from both groove and land areas or itis formatted so as to record/read in/from only either of the groove andland areas. For a substrate formatted so as to record information onlyin the groove area, the track pitch should preferably be around 0.7times the NA of the wavelength/focusing lens and the groove width shouldpreferably be around ½ of the value.

[0107] (Recording Laser Power)

[0108] An electric current flows in the recording medium in thisembodiment when in recording, so that a low laser power is usable torecord information. For example, when the recording linear speed is 15m/s or over, the laser power comes to exceed 10 mW for ordinaryrecording media. In this embodiment, however, the recording laser powercan be set over 2 mW and under 2 mW. The optimal recording laser powerdiffers among flown electric current values.

[0109] (Reading Laser Power)

[0110] On the other hand, the present invention employs a laser powerthat can cope with processes with a sufficient margin. Therefore, thelaser power can be raised when in reading to obtain a preferable readsignal S/N ratio even at a higher recording density so as to reduce theinfluence by both laser and system noises. As described above, therecording medium in this embodiment enables an electric current to beflown therein when in reading, so that information comes to be recordedin the medium with less light absorption by the recording layer, and alarge thermal diffusion, and a low recording sensitivity. Occurrence ofread errors can also be suppressed even at a high reading laser power.For example, it is possible to set 2 mW for the recording laser powerand 3 mW for the reading laser power.

[0111] When a 4-element array laser is used as the laser power supply,the data transfer rate can be improved by nearly four times faster thanever.

[0112] <Second Embodiment>

[0113] This second embodiment relates to a multi-layer recording mediumand a recording apparatus that uses the medium.

[0114]FIG. 16 shows a structure of the recording apparatus around therotary shaft in this embodiment. As described with reference to theblock diagram of the applied voltage reversing and controlling circuitin FIG. 15, the recording apparatus supplies both plus and minusvoltages and recording medium layer selection signals to three sliprings 72 to 74 of the rotary shaft. The maximum current applied to therotary shaft from the circuit substrate of the recording apparatus canbe reduced even when in fast coloring/decoloring by charging the currentin a capacitor once, since the coloring/decoloring time is shorter thanthe recording time. The circuit that includes such a capacitor as shownin FIG. 15 is built in the hollow space of the disk receiving part 78and the wiring to each layer shown at the right end side of the blockdiagram is connected to the corresponding one of the rotary shaftelectrodes 75 to 77 through the applied voltage reversing andcontrolling circuit. There are eight electrodes in this circuit andother five electrodes are disposed on a hidden surface (not shown here)of the rotary shaft. Consequently, a plus voltage is applied to a layerto be colored while a minus voltage is applied to the layer when it isdiscolored. Only the plus voltage may be applied from the circuitsubstrate of the recording apparatus to the rotary shaft. In this case,both plus and minus voltages are generated by a circuit built in thedisk receiving part.

[0115] The basic structure of the recording medium in this embodiment isthe same as that in the first embodiment, but the recording layer ismade of an electro-chromic material that is to be colored by an appliedvoltage. As shown in FIG. 11, the medium is 12 cm in diameter and 0.6 mmin thickness. The medium has a tracking groove formed at track pitchesof 0.45 micron, a depth of 23 nm, a width of 0.23 micron and used forin-groove recording. The medium is fabricated by stacking electrodes andlayers on a polycarbonate substrate 89 that holds address information aswobbles of the above groove in order of an Ag₉₄Pd₄Cu₂ half-transparentreflection layer 81, an ITO transparent electrode 82, an electro-chromicmaterial layer 83, an ITO transparent electrode 84, a ZnS.SiO₂ insulatorlayer 85, an ITO transparent electrode 86, an electro-chromic materiallayer 87, an ITO transparent electrode 88, a ZnS.SiO₂ insulator layer,an ITO transparent electrode, an electro-chromic material layer, an ITOtransparent electrode, a Zn.SiO2 insulator layer, an ITO transparentelectrode, an electro-chromic material layer, and an ITO transparentelectrode (four electro-chromic material layers are stacked such way).Furthermore, a polycarbonate substrate 90 that is 120 mm in diameter and0.6 mm in thickness is stacked on the stacked layer. The laser beam isapplied to the target on the medium from this protective substrate side.The electro-chromic material layer consists of two or three layers. Whenan electro-chromic layer consists of three layers, concretely, it comesto consist of a 150 nm thick lrOx or NiOx (x: a positive number of 1orunder) layer that is an oxide coloring type first coloring layer, a 300nm thick Ta₂O₅ layer that is a fixed electrolyte layer, and a 200 nmthick WO₃ layer that is a reduction coloring second coloring layer. Whenan electro-chromic layer consists of two layers, it comes to consist ofa 200 nm thick OH ion tank layer consisting of Cr₂O₃ and a 200 nm thickcoloring material layer consisting of WO₃. The transparent electrodefarthest from the light incident side may be replaced with such ametallic electrode as W—Ti. When an electro-chromic material layer isformed by coating, the groove is filled step by step by stacked layers,so that the distance between electrodes differs between the land areaand the groove area at both sides of the recording layer; the distancebetween the recording layer and the land area is shorter than thatbetween the recording layer and the groove area. However, the distancebetween electrodes is not so long between them as that one of theelectrodes is almost flattened just like in the first embodiment or oneof the insulator layers is assumed as an insulator layer having athrough-opening.

[0116] The above stacked layer is over-coated by UV-curing resin and thedisk is put together with another similar disk.

[0117] Then, a voltage is applied to the transparent electrodes disposedat both sides of the target recording layer from/in which information isto be recorded/read while a laser beam having a wavelength of 400 nm isirradiated to the target layer. Only the layer is then colored and thelaser beam is absorbed/reflected from the layer, thereby information isrecorded/read selectively therein/therefrom. There is no need to limitthe voltage so as to be applied only to one recording layer at thistime. When an array laser beam is used to record information in aplurality of recording layers simultaneously, the voltage is applied tobetween a plurality of pairs of electrodes. If the voltage to be appliedto between electrodes in a non-target recording layer in which noinformation is to be recorded is set to a limited value (not 0), it isprevented to take much time to color the layer due to the capacitancebetween electrodes and the response speed of the material to be colored.If a reverse voltage is applied to a layer to be decolored by stoppingthe voltage application, the decoloring time is reduced to ½ or under.

[0118] Recording in the medium of the present invention is done asfollows. The electro-chromic function of the recording film is disabledby a laser beam and/or electric current so that the layer is not coloredor it has an absorption spectrum different from that before therecording. The recording density of the film may be changed by the laserbeam for recording. There are also other recording methods; for example,the recording layer is stacked on another layer, which is made of anorganic or non-organic material in which at least one of therefractivity and the reduction coefficient is changed due to a physicalchange (ex., phase-change) or chemical change (ex., reaction to Li-ion)by a heat or electric current. Then, the recording is done according tosuch a change in this layer. For example, a phase-change recording filmcomposed of In₅₀Se₄₅T₁₅ is preferable, since the transmissivity is highwith respect to a laser beam having a wavelength of 780 nm or 660 nm,especially a laser beam having a wavelength of 780 nm. When inrecording, the medium is heated indirectly due to the light absorptionby the electro-chromic material layer. While the size of theelectro-chromic material layer depends on the used material, the layerhas photo-conductivity. The layer can thus be heated effectively by theelectric current of the photo-carrier. In the case where the mediumincludes a phase-change recording layer, crystallization ornon-crystallization occurs in the layer when the layer is heated. As aresult, the phase of the recording layer changes. However, in the casewhere the medium is designed so that the refractivity caused by aphase-change is recognized easily, especially as a reflectivitydifference when the electro-chromic layer is colored, information can beread from each of the multi-layer recording films independently. And, ifthe optical film thickness between transparent electrodes is setapproximately so as to become equal to the wavelength of the readinglaser beam, all the recording layers become equal to each otheroptically.

[0119] A voltage may be applied to a plurality of layers simultaneouslyor sequentially so as to color those layers when in recording and/orreading in/from them. If the thickness of each layer formed betweentransparent electrodes is set equally to the focal depth of the focusinglens approximately so that the layer is colored according to the lightabsorption coefficient set larger for the deeper-disposed layer, it ispreferable to move the focal point in the depth direction to enable highdensity recording. If each layer is a little more thinned, the mediumwill be suited for volume hologram recording. Almost the same lightabsorption coefficient may be set for all the layers that are morethinned so that a high power laser irradiation is done on all the layersincluding the deepest one, thereby recording is done from those layerswhile a low power laser is irradiated only to a layer closer to thelight incident side, thereby recording is done only in the layer. Thismethod enables multi-value recording. Furthermore, the present inventionmakes it possible to differ the light absorption coefficient amonglayers when in recording and reading. When in recording, if the voltageapplying time for coloring is changed for each layer so that the lightabsorptivity is set for each layer like 20%, 30%, 40%, and 50%differently among layers and the light absorptivity is fixed at 20% foreach layer when in reading, the light reflected from the Ag—Pd—Cu layercomes to include the information of each layer in uniform. This is verypreferable.

[0120] If all the stacked layers are divided into some groups, forexample, if the four layers are divided into two groups so that eachconsists of two layers in this embodiment and the electro-chromic layersin the same group are colored/decolored simultaneously, thecoloring/decoloring time is shortened. And, the recordingcharacteristics will be more improved if the voltage and/or the dilutionof the electro-chromic material with acrylic polymer is adjusted so thatthe farther the layer is disposed from the light incident side, thehigher the light absorptivity becomes in the same group as describedabove.

[0121] There is also another method for controlling thecoloring/decoloring time so as not to limit the recording/reading speed.According to this method, the layers are colored sequentially from theother side to this side at a view from the light incident side anddiscolored in the reverse order. Consequently, while a layer is colored,a voltage can be applied to the next adjacent layer to be colored. Thecoloring is thus speeded up.

[0122] As the electro-chromic material, such organic materials asthiophene organic olygomer and polymer typically as shown in FIG. 12 areusable in addition to WO₃. Especially, conductor organic materials wouldbe better. For a thiophene molecule polymer, however, the laserwavelength is set at 660 nm and the track pitch is set at 0.6 μm, whichis about double the ordinary value. A thiophene material polymer isformed by vacuum deposition, electrolytic polymerization, or coating. Inthe case where the electrolytic polymerization is employed,poly(3-methylthiophene), which is a thiophene derivative, is used asmonomer. And, LiBF4 is used as the supporting electrolyte andbenzonitrile is used as the solvent.

[0123] In this connection, the electro-chromic material layer comes toconsist of the following three layers; a layer used as both ion storagelayer and dark-current blocking layer, which consists of(CeO₂)₆₇(TiO₂)₃₃; a solid electrolytic layer made of a material in whichacryl UV curing resin is mixed with Li-triflate (official name:Li-trifluoromethansulfonate: CF₃SO₃Li) and a plasticizer; and a PEDT/PSSlayer, that is, an electron activation conductor polymer coloringmaterial layer made of a material in which poly (3,4ethylenedioxythiophene) and poly (stylene sulfonate) are mixed. Beforethe thiophene polymer is formed, one of the ciano-group, the thiolgroup, and the S-asetyl group is added to the end portion of thethiophene molecule polymer. This is to have the longitudinal directionof the thiophene molecule polymer oriented in the film thicknessdirection, thereby having the current flown easily in the direction. Forthe organic solid electrolyte layer,polyethyleneoxide-thio-potacium-cyanate will be most suited. The abovethree layers are among those described as coloring control window glassmaterials and layers in the paper titled as “electrochromic Window Basedon conducting Poly (3,4-ethylenedioxythiophene)-Poly(styrene sulfonate”in “Advanced Functional Materials vol.12, No.2 pp.89-94 (February 2002)written by Mr. Helmut W. Heuer, et al.

[0124] The above-described PEDT/PSS layer may be replaced with SPEB. TheSPEB is an electrochromic coloring polythiophene polymer materialdescribed in the paper written by Mr. Fei Wang, et al in Micromoleculesvol.33 pp.2083-2091 (2000) Electrochromic Linear and StarBranched poly(3,4-ethylenedioxychiophene-didodecyloxybenzene) polymers. As a result,the coloring and decoloring can be more speeded up. The polymersynthesizing method and the film forming method are the same as thosedescribed in the above paper, but the above-described solid electrolyteis used as the electrolyte in this embodiment.

[0125] The solid electrolytic layer and the coloring material layer,which is made of an electron-active conductive polymer, are formed bypolymerization underelectric-fie of a poly-thiophene layer. For example,the two layers can be united into one by implanting such the dopant asLi-trifrate in the layer. Such an organic material layer becomesconductive and the conductivity rises in proportion to a temperaturerise. The layer can also have photo-conductivity, thereby thephoto-carrier is accelerated by an electric field to improve therecording sensitivity upon a temperature rise and there is no need toinput/output water in/from the film for coloring/decoloring, which isrequired for the WO3. A layer is colored by the electrons driven intomolecules to be excited by a light. In order to neutralize this movementof electrons, such ions as Li are moved. The use of such an organicmaterial layer also includes the following disadvantage; the filmforming speed is slow and it is difficult to form large-area films. Inorder to solve this problem, monomer or low molecular weigh consistingof only a few linked molecules should be vacuum-deposited rapidly so asto be transformed into origomer on the substrate. This origomer formingprocess is performed by irradiating a blue or near-UV ray the targetmolecules so as to excite them during a vacuum-depositing process. Forthe origomer forming process, the following materials are usable;polymer of thiophene derivative (abbreviated as poly-thiophene), as wellas such metallic phthalocyanin as Lu-di-phthalocyanin, peptyl-viologen,styril compound tungsten, 3,3 dimetyl-2-(P-dimethyl aminostyril)indorino[2,1-b] oxazorin (IRPDM) (light source wavelength: 5145 nm) and3,3 di-metyl-2(P-di-metyl aminocynnamiridenvinyl) indorino[2,1-b]oxazoril that are styril compounds. In addition, the film may be formedby coating.

[0126] Furthermore, in order to provide the medium with aphoto-conductor effect, a TCNQ (7,7,8,8-Tetracyanoquinodimetohane) layermay be formed therein. Even when those organic matters are used, otherportions of the disk are formed just like in the above embodiment.

[0127] Instead of the WO₃ organic material, any of pllucianblue(KxFe^(II)yFe^(III)z(CN)₆, MoO₃, NbO₅, V₂O₅, TiO₂, NiOOH, CoOOH, Rh₂O₃,IrOx (x: a positive number under 1), ZrNCl, lnN, SnNx (x: a positivenumber under 1), MnOx (x: a positive number under 2), and WO₃-MoO₃compound (mixture) films may be usable.

[0128] When most of the positive ions are moved out of a predeterminedplace in any of such metals as Li and hydrogen or when most of theelectrons existing in the base state of a light spot are excited due toan applied current, the electro-chromic material causes the lightabsorption to be reduced automatically, thereby the current flow is aptto be disturbed. It is thus prevented that a large current flows in thewhole disk and/or an excessive current flows in the light spot,resulting in excessive growth of recording marks. In other words, thefollowing phenomenon occurs; when a laser beam is irradiated to betweenthe first and second electrodes while a voltage is applied thereto, thecurrent in the irradiated spot increases. And, if a voltage is keptapplied thereto even after the end of the laser irradiation, the currentdecreases in a certain time, then the recording layer (electro-chromiclayer or the like) status changes. The current might thus decreaseautomatically during the laser irradiation.

[0129] The electro-chromic material layer may be replaced with a layermade of a material in which an electro-luminescent (EL) material and aphoto-chromic material are mixed. The color of the photo-chromicmaterial is changed by a light emitted from the EL material, therebylight absorption occurs due to the recording or reading laser beamwavelength. Usable EL materials are such non-organic materials as ZnO orthe like, as well as organic materials. The organic material may be, forexample, a combination of the photo-chromic material and a materialwhose emitted light wavelength is equivalent to that used to change thecolor of any of such photo-chromic materials as diarylethene, fulgide,etc. selected from among the organic EL materials described on pp.3 to22, No.2, vol.33 of the R&D Review published by Toyota Chuo Kenkyu-sho.For a layer made of any of those organic materials, thevacuum-deposition, vapor phase deposition, and coating methods areemployable. When coating is selected, the material is thinned enough bya solvent so that the film thickness difference is almost eliminatedfrom between the groove areas. An organic EL material consists of anelectron layer or hole transfer layer and a luminescent layer material.A tri-phenyl amine material is included in the EL material when theefficiency is improved. The hole transfer layer material may be, forexample, star-burst amine (m-MTDATA) (film thickness: 60 nm) obtained byshaping tri-phenyl amine into star-like molecules and the luminescentlayer material may be benzo-oxasol Zn complex (Zn(BOX)₂) (filmthickness: 40 nm) is used to develop the color.

[0130] The photo-chromic material may be any of fulgide, diarylethene,etc. as shown in FIG. 12. When fulgide is used, the light absorptionoccurs around a wavelength of 500 nm due to an irradiated blue laserbeam. A Kr laser having a wavelength of 514.5 nm is thus usable forrecording.

[0131] For small-sized recording media in which a high sheet resistanceis not regarded as a problem, any of such conductive polymers aspolyacethylene, polychiophene, etc. is usable to form transparentelectrodes. This is favorable, since the refractivity related toelectro-chromic material layers is smaller than that of non-organictransparent electrodes, so that the adverse interference by the lightreflected from the boundary layer is avoidable. As a ground layer, alayer made of a hydrophobic surface treatment, a silane coupling agent,or thin copper element (Cu, Ag, Au) having an average film thickness of0.5 to 3 nm may be formed.

[0132] Similarly, the heat insulator layer should preferably be formedwith an organic material in the optical point of view. The insulatorlayer may have conductivity, but it should preferably not. Many morematerials such as acryl-derivative origomer, polymer, andmetal-phthalocyanine vacuum-deposited film are usable for the insulatorlayer.

[0133] Furthermore, organic materials used for EPD, that is,electrophoresis display media, or a conductive organic material layerwhose absorption edge changes according to a temperature rise caused bythe current may be used.

[0134] A phase-change material layer may also be used as a recordinglayer. For example, in the case where a red laser power source is used,a phase-change recording layer that includes such Se as ln—Se, ln—Se—Tl,or the like by 30 atomic % or over does not absorb the laser beam somuch and its phase changes due to the indirect heating by the lightabsorption by the electro-chromic layer and/or the current action. Thephase-change recording layer has a high refractivity, so that the filmthickness of the transparent electrodes should be decided so as toprevent the light reflection from the boundary surface.

[0135] Every multi-layer film may be formed within the focal point ofthe focusing lens, but it is also possible to dispose a 20- to 40-micronthick spacer layer between layer groups consisting of several layersrespectively to change the focal point to record/read informationin/from each layer. In this case, when two or more spacer layers are tobe used, the optical system should be provided with an element thatcompensates the spherical aberration.

[0136] The recording/reading method in this second embodiment is thesame as that in the first embodiment.

[0137] <Third Embodiment>

[0138] In this third embodiment, as shown in FIG. 14, the laser 91 isattached on a surface slightly inclined from the right angle of therotary shaft of the mirror driving motor 95 so that the laser beam 93 isreflected so as to be moved in a circular or elliptic pattern by themirror 94 that rotates fast. A light spot is then formed by a 4×6reflection mirror array 97 made of a silicon crystal in accordance withone of the MEM techniques, thereby information is recorded in the mediumfast without moving the recording medium fast. In FIG. 14, referencenumerals are defined as follows; 92 denotes a lens, 96 denotes an arrayselection mirror, 98 denotes a Si wafer, 99 denotes a cross sectionalview of a recording layer film. The shape of the entire medium is notdisk-like, but it is rectangular. Each mirror is driven by anelectrostatic or electromagnetic force generated from a transistor arraydisposed just under the mirror.

[0139] Many cone-shaped recesses are formed and disposed regularly inboth vertical and horizontal directions similarly to the process forforming an ordinary original optical disk. The recesses are 1um indiameter and 0.4 μm in depth. The distance between the centers of thoserecesses is set at 1.5 μm. The cross sectional view of the recesses at aplane parallel to the substrate may be slightly elliptic. On thissubstrate are formed four layers by means of spattering in order of aheat dispersing Ag94Pd4Cu2 layer (thickness: 50 nm), a ZnS.SiO2protective layer (thickness: 50 nm), a Ge—Sb—Te recording layer(thickness: 30 nm), and a ZnS.SSiO₂ protective layer (thickness: 50 nm).Finally, an Al₉₈Ti₂ electrode layer is formed at a thickness of 70 nm onthe stacked layer. Furthermore, a 100 μm thick polycarbonate sheet isstacked thereon with UV-curing resin therebetween. After the UV-curingresin is cured/bonded, the sheet is removed. The stacked film on theflat surface is thus removed and the stacked film only in thecone-shaped recesses are left, thereby the cross section 99 of thestacked layer is exposed. Information is recorded in this crosssectional portion. If the substrate surface is activated beforehand bymeans of UV ray irradiation, the entire Ag alloy layer, which is thefirst stacked layer, is left together with that on the flat portion ofthe substrate. The left-over portion can be used as an electrode. Afterthe cross sectional portion 99 is exposed, a 30 nm thick SiO₂ layer anda 70 nm thick ITO transparent electrode layer are formed thereon. As aresult, almost no SiO₂ layer is stacked on the slope to each cone-shapedrecess and the transparent electrode film comes in contact with the topelectrode layer directly. The laser beam can thus be irradiated to thecross sectional portion 99 to assist the recording there while a voltageis applied to between the bottom Ag alloy and the top ITO layer. Whenthe upper insulator layer is not put in contact with any transparentelectrode, the protective layer of the cross sectional portion 99 isetched by dilute acid quickly, then a thick TiO₂ layer is formed in thecross sectional portion 99. The TiO₂ layer then becomes a solidimmersion cylindrical lens built in the barrel-shaped medium, therebythe laser beam is condensed enough and irradiated on the cross sectionalportion 99 of the recording layer.

[0140] The Ge—Sb—Te recording layer may be replaced with a stacked filmconsisting of the thiophen polymer or WO₃ electro-chromic material layerdescribed in the second embodiment to obtain satisfactorycharacteristics. Recording is done by damaging the coloring capabilityof the electro-chromic material layer by a heat.

[0141] On the other hand, it is also possible to form grooves on thesubstrate surface and record information in the grooves just like therecording on conventional optical disks. In this case, eight grooves areformed in parallel to the disposed reflection mirror arrays. Theinterval for disposing the reflection mirror arrays is double that ofgrooves. By changing the angle of each of those mirrors, recording canbe made in either of the two grooves. Usually, recording is done in oneof the grooves, then in the other. The recording medium in this thirdembodiment has a multi-layer structure just like in the secondembodiment. The material used for each layer may be any of organic andnon-organic materials as described in the second embodiment. The groovemay not be shaped linearly; it may be formed like a concentric circle orspiral under each mirror.

[0142] In any of the above cases, each portion of the target layer maybe irradiated not via a mirror array, but via a moving mirror.

[0143] If a four-element array laser power source is used, the laserbeam is irradiated on the upper four mirrors simultaneously to speed upthe data transfer by nearly four times.

[0144] The number of reflection mirror arrays can be increased up toabout 1000×1000 when a large capacity is required.

[0145] The recording and reading methods in this third embodiment arethe same as those in the first embodiment.

[0146] Our invention also includes the following.

[0147] 1. An information recording apparatus for recording informationin said information recording medium by means of irradiation of a lightfocused on said medium, said apparatus including:

[0148] a rotary shaft for rotating said medium; and

[0149] a motor for rotating said rotary shaft;

[0150] wherein a plurality of electrodes are disposed at said rotaryshaft or a portion of a disk receiving part attached to said rotaryshaft, adjacent to the center hole of said medium.

[0151] 2. The information recording apparatus according to above 1;

[0152] wherein said rotary shaft has positioning means used to fix aposition of said disk relatively with each of said plurality ofelectrodes.

[0153] The information recording medium of the present inventiontherefore enables a high electric field to be applied in a narrow range,thereby the medium turns fast to enable fast recording and high densityrecording permissively to both auto-focusing and tracking offsetoffsets.

[0154] Furthermore, the information recording medium enables many morelayers to be stacked than any conventional media, so that the practicalrecording density is improved and the recording capacity per medium isexpanded significantly.

What is claimed is:
 1. An information recording medium for recordinginformation by means of light irradiation, including at least: asubstrate; a first transparent electrode formed on said substrate; arecording layer including an electro-chromic material and formed on saidfirst electrode; and a second transparent electrode formed on saidrecording layer; wherein said recording medium further includes one ormore additional recording layers each including an electro-chromicmaterial formed between transparent electrodes, said one or morerecording layers being different from said farthest one from the lightincident side.
 2. The recording medium according to claim 1; whereinsaid electro-chromic material is a conductive electro-chromic material.3. The recording medium according to claim 1; wherein a phase-changerecording layer is formed between said recording layer and either ofsaid two transparent electrodes on both sides.
 4. The recording mediumaccording to claim 1; wherein a photo-conductor layer is formed betweensaid recording layer and either of said two transparent electrodes onboth sides.
 5. The recording medium according to claim 1; wherein saidmedium is circular in form and has a third electrode that is long in theradial direction of said medium and narrow, said third electrodesupplying an electric current to said first and second electrodes. 6.The recording medium according to claim 1; wherein at least either ofsaid transparent electrodes on both sides of the recording layer isdivided into a plurality of electrodes.
 7. The recording mediumaccording to claim 4; wherein a conductor layer is formed between saidrecording layer and said photo-conductor layer, said conductor layerhaving a thickness of 1 nm to 10 nm.
 8. The recording medium accordingto claim 1; wherein the capacitance between said first and secondelectrodes is over 0.01 F to 0.1 F.
 9. An information recording mediumfor recording information by means of light irradiation, including: asubstrate; a first conductor film formed on said substrate; an insulatorfilm formed on said first conductor film and having a through opening; arecording film formed so as to be extended from said through openingonto said insulator film and enabled to record information therein; anda second electrode formed on said recording film.
 10. The informationrecording medium according to claim 9; wherein a photo-conductor film isformed between said recording film and said second electrode.
 11. Theinformation recording medium according to claim 9; wherein said mediumhas a land area and a groove area in the radial direction thereof;wherein said recording film is formed over said through opening existingin either said land area or groove area; wherein said insulator filmexists in the other of said land and groove areas; and wherein thedistance between said first and second electrodes at a portion differentfrom said through-opening is 1.1 or more when the distance between saidfirst and second electrodes in said through-opening is
 1. 12. Theinformation recording medium according to claim 9; wherein saidinformation recording medium has a land area and a groove area in theradial direction thereof; wherein said recording film is formed oversaid through-opening existing in one of said land area and said groovearea; where said insulator film exists in the other of said land areaand said groove area; and wherein the distance between said first andsecond electrodes in a portion different from said through-opening is 2or more when the distance between said first and second electrodes insaid through-opening is
 1. 13. The information recording mediumaccording to claim 1; wherein said electro-chromic material is atungsten oxide or thiophene derivative material.
 14. An informationrecording method for recording information in a plurality of spots on aninformation recording medium by means of light irradiation, said mediumincluding at least a substrate; a first conductive film formed on saidsubstrate; a recording layer formed on said first conductor film made ofan electro-chromic material; and a second conductor film formed on saidelectro-chromic material layer.
 15. The information recording methodaccording to claim 14; wherein said information recording medium recordsinformation therein by applying a voltage at least to two of a pluralityof electrodes formed by dividing one of said first and secondelectrodes.
 16. The information recording method according to claim 14;wherein said information recording medium has a plurality ofelectro-chromic material layers formed between electrodes respectively;and wherein said medium applies a voltage to the electrodes disposed atboth sides of a predetermined one of said plurality of electro-chromiclayers to record information in said predetermined electro-chromicmaterial layer, said voltage being different from that applied to theelectrodes disposed at both sides of other recording films.
 17. Theinformation recording method according to claim 14; wherein a light isirradiated to between said first and second electrodes while a voltageis applied thereto and said voltage is kept applied even after the endof said light irradiation.